Revert "CI: Update CEF hash for Flatpak to fix crash"

This reverts commit 7bf7c01ff1b45e5e6c295982f89cfae896e94d8d.

The f639d8923 CEF wrapper fails to build on Ubuntu 18.04 due to
outdated glibc, and Jim's recent commits seem to solve the shutdown
assert. For now, revert to the known functional build.

CI/flatpak/com.obsproject.Studio.json

@@ -259,7 +259,7 @@
         {
           "type": "archive",
           "url": "https://cdn-fastly.obsproject.com/downloads/cef_binary_4638_linux64.tar.bz2",
-          "sha256": "f639d8923be42730419d703259125a3dd5349c6eb2b4d6381dd7e766500629ef"
+          "sha256": "3c7707b13ca99c220e1650381f3d301c016f5c6ed6f478b83223645031fb13b9"
         }
       ]
     },